The present invention relates generally to communication systems, and, more particularly, to generating a stable reference clock for carrier frequency generation in such systems.
Communication systems, such as wireless communication networks, typically comprise disparate pieces of interconnected communications equipment to provide overall system functionality. Coordination and synchronization of the different communication system elements is an important and challenging aspect with regard to the design of the overall communication system.
Oftentimes, communication systems are arranged in a hierarchical fashion, with a master component providing overall synchronization and control for subordinate elements within the system. For example, in a wireless communication network, a mobile switching center (MSC) is often used to interface one or more base stations with various other networks, such as the Public Switched Telephone Network (PSTN). T1/E1 communication links, based on pulse code modulation (PCM), allow signaling and control between the various elements in a wireless communication network. Additionally, the T1/E1 data clock serves as a common time base for various elements in the system, and thus can be used to maintain overall system synchronization.
At least one timing-based function within the typical wireless communication network is subject to particularly stringent accuracy requirements. This function involves generation of the transmit carrier frequencies that are used in the transmit signals broadcast within the wireless communication network service area. The Federal Communications Commission (FCC) mandates strict limits for carrier frequency generation error to minimize interference. While the T1/E1 specification defines a relatively accurate and stable data clock, the specification permits maximum allowable errors for certain types of clock deviations that are in excess of the maximum errors permissible if the T1/E1 clock is used as a reference for carrier frequency generation.